This invention relates to a transmission system adapted for both synchronous and asynchronous data transmission and more specifically to a circuit for automatically adapting to the proper transmission mode.
A modem is a device used at the receiving and transmitting ends of a telephone line to process data transmission over that line. Data moving through the modem can be either synchronous, meaning that data characters are transmitted at a fixed rate, with the transmitter and receiver synchronous or asynchronous, meaning that time intervals between transmitted characters may be of unequal length.
A host computer that provides dial-up facilities for both asynchronous applications (e.g., data from a remote terminal), and synchronous applications (e.g., file transfer data from another host computer) would ordinarily have one modem port for asynchronous data and a separate modem port reserved for synchronous data.
Typically, each modem port of the host computer would receive data on a separate communication line from the telephone switching office. In certain applications, however, data traffic for each port is of sufficiently low volume that the cost of a separate communication line and modem cannot be justified. Modems are designed with options to handle either synchronous data or asynchronous data but not both. Thus, using present modem designs (some have a manual switch for converting from one mode to another), the desired result of using a single communication line for different data types is not achievable.